The present invention relates to a base oil for a lubricating oil and a lubricating oil composition containing said base oil, for a mechanical apparatus with an orifice. More particularly, it is concerned with a base oil for a lubricating oil and a lubricating oil composition containing said base oil, which are to be used in various mechanical apparatuses with orifice mechanism and are excellent in working properties at low temperatures.
2. Description of Related Art
In various mechanical apparatuses with orifice mechanism, for example, oil pressure machines such as a shock absorber for automobiles, a door closure and the like, and an automatic feeding apparatus for switching railway points, a lubricating oil the pour point of which is controlled to about -35.degree. C. in view of working properties at low temperatures, by compounding a large amount of a pour point depressant to a base oil having a relatively low pour point (about -15.degree. C.) has heretofore been used.
The above lubricating oil, however, is increased in oil resistance at low temperatures and suffers from various disadvantages. For example, when the lubricating oil is used in a shock absorber, its low temperature damping force (damping capacity) is decreased; when the lubricating oil is used in a door closure, its working properties are reduced; and when the lubricating oil is used in an oil feeding apparatus for switching railway points, an oil cannot be fed at low temperatures. Another disadvantage is that the performance of the lubricating oil markedly varies with a lapse of time, because the polymer (e.g., polymethacrylate) compounded in a large amount as a pour point depressant is subject to mechanical shear.